2009 Rough Idle and Stalling After Fuel Pump Replacement
07-05-2020, 05:03 PM
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2009 Rough Idle and Stalling After Fuel Pump Replacement
I have read through most of the different threads on here and could not find the smoking gun to my system. I was hoping someone could point me in the right direction so I am not just throwing parts at this problem.
My wife has a 2009 957 with the VR6. It was running great up to a week or so ago. When she came home, I could smell gas, and via information on this thread I tracked down a leak from the crack on top of the fuel filter. No big deal, I ordered the a replacement filter. When I ordered the filter, there was a deal on the passenger side fuel pump, so I figured I would snag it and throw it in, while I was in there. After quickly realizing a spaghetti monster lived inside the tank, I spent some time figuring out all the hoses, and I was pretty confident everything was hooked up as it should be.
Started it up, and it ran and idled like crap. I attempted to drive it around the block, and it was stalling and struggling to go. I thought maybe there was some air in the system, but I drove it far enough any air should have been pushed out, and there was not improvement or change at any time.
So, I thought maybe the new (discount) pump was faulty, so I just go ahead and order the pair of replacement pumps. They arrive, I install them. Making sure to to pay specific attention to the hose routing and confirming everything is crossed as it is supposed to be. I am extremely confident the hoses and wiring is correct. Start the vehicle, same conditions, even after a drive.
So at this point there is a new fuel filter, and new pumps in both locations. We decided to test the regulator. Using an air compressor and a gauge, we confirmed the valve opens around ~75psi. After installing it back on the tank, we put the gauge on the output line to engine, and we were getting ~80psi on that line. I am surprised that the line pressure is that high, or high at all just given that the fuel line feeds a high pressure pump. My understanding is that the pressure between the fuel pressure regulator (FPR) and the high-pressure fuel pump (HPFP) should be 55+/-3psi at idle, if my digging around on here is correct. And my fuel pressure is clearly above that range, which leads to indicate a faulty FPR. It seems like chance that the FPR would be fine until it was removed to install the pump, but I have ordered a new one, which is supposed to be delivered at the end of the week.
I was hoping someone could confirm some things with me. I do not want to wait a week for a part to arrive to find that this is not the root issue, and I needed to look else where or order a different part. Can having a 80PSI fuel line pressure to a pump that puts over 10x that pressure out to the injectors really cause the vehicle to run this poorly? I can confirm the vehicle is running rich, that both pumps are running correctly, and that pulling the 20A fuse for the fuel pumps individually made no difference in pressure or in how the vehicle ran.
Is there anything that can happen during a fuel pump replacement that could cause this issue? I saw a thread where someone had to go to the dealer to have their "fuel system reset" and I cannot even image what that could mean. The battery was unplugged during installation, and I don't know how the vehicle could tell that pumps were replaced. And the vehicle fuel trims should have been reset anyway.
I would love it if anyone could be a fresh set of eyes on this, and maybe let me know if this sounds like something the FPR will fix, or if I need to look into something else.
Thank you.
My wife has a 2009 957 with the VR6. It was running great up to a week or so ago. When she came home, I could smell gas, and via information on this thread I tracked down a leak from the crack on top of the fuel filter. No big deal, I ordered the a replacement filter. When I ordered the filter, there was a deal on the passenger side fuel pump, so I figured I would snag it and throw it in, while I was in there. After quickly realizing a spaghetti monster lived inside the tank, I spent some time figuring out all the hoses, and I was pretty confident everything was hooked up as it should be.
Started it up, and it ran and idled like crap. I attempted to drive it around the block, and it was stalling and struggling to go. I thought maybe there was some air in the system, but I drove it far enough any air should have been pushed out, and there was not improvement or change at any time.
So, I thought maybe the new (discount) pump was faulty, so I just go ahead and order the pair of replacement pumps. They arrive, I install them. Making sure to to pay specific attention to the hose routing and confirming everything is crossed as it is supposed to be. I am extremely confident the hoses and wiring is correct. Start the vehicle, same conditions, even after a drive.
So at this point there is a new fuel filter, and new pumps in both locations. We decided to test the regulator. Using an air compressor and a gauge, we confirmed the valve opens around ~75psi. After installing it back on the tank, we put the gauge on the output line to engine, and we were getting ~80psi on that line. I am surprised that the line pressure is that high, or high at all just given that the fuel line feeds a high pressure pump. My understanding is that the pressure between the fuel pressure regulator (FPR) and the high-pressure fuel pump (HPFP) should be 55+/-3psi at idle, if my digging around on here is correct. And my fuel pressure is clearly above that range, which leads to indicate a faulty FPR. It seems like chance that the FPR would be fine until it was removed to install the pump, but I have ordered a new one, which is supposed to be delivered at the end of the week.
I was hoping someone could confirm some things with me. I do not want to wait a week for a part to arrive to find that this is not the root issue, and I needed to look else where or order a different part. Can having a 80PSI fuel line pressure to a pump that puts over 10x that pressure out to the injectors really cause the vehicle to run this poorly? I can confirm the vehicle is running rich, that both pumps are running correctly, and that pulling the 20A fuse for the fuel pumps individually made no difference in pressure or in how the vehicle ran.
Is there anything that can happen during a fuel pump replacement that could cause this issue? I saw a thread where someone had to go to the dealer to have their "fuel system reset" and I cannot even image what that could mean. The battery was unplugged during installation, and I don't know how the vehicle could tell that pumps were replaced. And the vehicle fuel trims should have been reset anyway.
I would love it if anyone could be a fresh set of eyes on this, and maybe let me know if this sounds like something the FPR will fix, or if I need to look into something else.
Thank you.
07-05-2020, 11:30 PM
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Hi - scenerios I can imagine:
1. Defective fuel pressure regulator from the pumps allows excessive pressure at the input of the HPFP, which being a simple mechanical device over-pressures it's output, and puts the output pressure regulator out of range, resulting in too much pressure at the injectors and an overly rich mixture.
2. Defective HPFP - the regulator on the HPFP went bad and is allowing the overpressure condition.
I think you need to track down real numbers for the expected input pressure at the HPFP and then measure it. If the pressure is excessive that pretty much points to the fuel pressure regulator in the top of the tank.
Just one comment on all this - dunno if you're in the US - but I believe in the US Porsche has an outstanding recall to replace the filter and fuel pressure regulator on the first-generation Cayenne, due to fuel leakage around the top of both of these. It might be worth finding out if this is true - and see if it is - can you get Porsche to lend a hand fixing this.
BTW - welcome to the forum..
HTH,
1. Defective fuel pressure regulator from the pumps allows excessive pressure at the input of the HPFP, which being a simple mechanical device over-pressures it's output, and puts the output pressure regulator out of range, resulting in too much pressure at the injectors and an overly rich mixture.
2. Defective HPFP - the regulator on the HPFP went bad and is allowing the overpressure condition.
I think you need to track down real numbers for the expected input pressure at the HPFP and then measure it. If the pressure is excessive that pretty much points to the fuel pressure regulator in the top of the tank.
Just one comment on all this - dunno if you're in the US - but I believe in the US Porsche has an outstanding recall to replace the filter and fuel pressure regulator on the first-generation Cayenne, due to fuel leakage around the top of both of these. It might be worth finding out if this is true - and see if it is - can you get Porsche to lend a hand fixing this.
BTW - welcome to the forum..
HTH,
07-06-2020, 12:04 PM
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I did see the recall. I noticed that it applied to the gasket on this generation, especially 2008. I wasn't sure if it applied to my 09 or not. Overall the cost of the new gaskets, fuel filter, and the two pumps was not bad. I was surprised how much the FPR cost for how simple it is. I will just wait until the end of this week until that arrives, and hopefully it brings the tank output pressure back to within normal range and things go back to normal.
I was very surprised that those pumps are capable of putting out 80PSI.
If that does not resolve the issue, I suppose I will start making my way up the fuel pathway. Its surprising that everything would work normally until a crack formed, then all this would happen. But my old pumps were 11 years old with around 90K on them, so maybe the FPR was bad the whole time, but the pump output pressure was lower and that wasnt an issue.
I was very surprised that those pumps are capable of putting out 80PSI.
If that does not resolve the issue, I suppose I will start making my way up the fuel pathway. Its surprising that everything would work normally until a crack formed, then all this would happen. But my old pumps were 11 years old with around 90K on them, so maybe the FPR was bad the whole time, but the pump output pressure was lower and that wasnt an issue.
07-10-2020, 10:41 AM
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The new fuel pressure regulator came in, and I installed it with a new gasket. There was no change in how the vehicle behaved.
So, the next thing will be to look into the HPFP I think. I have no clue how all this could suddenly go bad by just replacing a cracked fuel filter.
So, the next thing will be to look into the HPFP I think. I have no clue how all this could suddenly go bad by just replacing a cracked fuel filter.
07-10-2020, 11:28 AM
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since the filters are not inline filters like on most cars, it's pretty much impossible to install it incorrectly. There is a tab that has to seat in place, and those plug and hose have to line up. I checked over all the hoses in the tank many times over. I am getting plenty of fuel and pressure out of the tank. So the issue has to be upstream now.
